Search for photon–photon elastic scattering in the X-ray region

We report the first results of a search for real photon–photon scattering using X rays. A novel system is developed to split and collide X-ray pulses by applying interferometric techniques. A total of 6.5×1056.5×105 pulses (each containing about 1011 photons) from an X-ray Free-Electron Laser are injected into the system. No scattered events are observed, and an upper limit of 1.7×10−24 m21.7×10−24 m2 (95% C.L.) is obtained on the photon–photon elastic scattering cross section at 6.5 keV.